No optimal solution for presbyopia exists at this time. Bifocals and progressive spectacles depend on shifting the direction of gaze, and thus severely limit the functional visual field.1 Existing contact lens-based solutions for presbyopia may also depend on shifting of gaze or on diffractive design, which divides light energy and reduces image quality and contrast.2
IOL solutions for presbyopia are also insufficient; based upon bifocal diffractive designs, they have high degrees of chromatic aberration, reduced mesopic and scotopic vision, and functionality only for near and far ranges mainly in the green wavelength.
There is no adequate treatment for severe irregular astigmatism either, especially in presbyopes. There cannot be a sufficient range of soft toric contact lenses to correct all refractive errors.
EXTENDED DEPTH OF FOCUS
In this paper, we present the all-optical Extended Depth of Focus Technique (EDOF; being developed and tested by Xceed Imaging, Ltd., Petach-Tikva, Israel)3,4 as an adjunct technology for use with spectacles, contact lenses, or IOLs. This technique is distinct from computer-based solutions. It seems to solve most of the problems associated with correcting presbyopia with regular or irregular astigmatism as well as correcting myopia and hyperopia with either form of astigmatism. Lenses embedded with EDOF technology enable simultaneous high-contrast images of near, intermediate, and distant objects—regardless of astigmatism and with no loss of visual field. Furthermore, the axially continuous-focused image does not have a set of discrete focusing planes, preserving light energy and preventing chromatic aberration.
The operating principle of EDOF technology is based upon generation of proper interference of the light rays passing through the lens' aperture. The interference is created by etching a fine concentric profile design (depth of less than 1 µm) around the optical axis on one surface of the lens. The interference created by the profile extends the depth of focus from 1.50 D in front to 1.50 D behind the focal point, for a total of 3.00 D. When added together in the focal plane, the rays generate a focal corridor of approximately 1 mm over an extended axial distance. Figure 1A shows the normal condition in presbyopia with the distant target in focus and the near target blurred. Figure 1B shows a similar eye with an EDOF structure, with both the far and near targets in focus due to the extension of the depth of focus.
The profile that generates the EDOF is relatively simple, and fabrication is cost effective. The structure has no small spatial variations. Therefore, its diffraction effects and chromatic dispersion are small and the energy efficiency is high. Unlike diffractive optical solutions, energy is not diverted into diffraction orders and away from the central order of interest. The EDOF technology can be used with spectacles, contact lenses, IOLs, and intracorneal implants.
Method. We tested results in 13 patients (eight myopic and five hyperopic presbyopes, seven of whom were astigmatic) who received soft contact lenses with the EDOF profile on their front surface. Patients underwent visual function testing before and while using the contact lenses. Visual acuity testing was similar to the testing described above for EDOF spectacle use. Results are presented in logMAR units.
Results. With as well as without the EDOF contact lens, the BCVA was close to zero. Before wearing the EDOF, distance corrected near visual acuity (DCNVA) was 0.5. With the EDOF, it was 0.11. The average astigmatism correction with the EDOF profile was 0.78 ±0.10 D.
Method. We studied 14 patients (five myopes and nine hyperopes) with spherical prescriptions ranging from -5.75 to 2.75 D. The average addition was 2.13 D (range, 1.50–2.50 D). With the exception of two patients with a spherical-only prescription, the range of astigmatic correction was 0.50 to 1.00 D. Results are presented in logMAR units.
The field of view was tested by displacing various Snellen letters along the field of view while the head of the patient was fixated. The patients had to identify every displaced letter and their answer were classified into one of four possible responses, with assigned scores from one to four: (1) choosing the identical letter to the one displayed, (2) choosing a similar letter to the one displayed, (3) choosing a letter not similar to the one displayed, or (4) not recognizing the letter.
Results. As in the EDOF contact lens case, with as well as without the EDOF lens, the BCVA was close to zero. Before wearing the EDOF lens, DCNVA was 0.465. With the EDOF lens, it was 0.079. Additionally, correction was demonstrated in up to 2.00 D of astigmatism, including irregular ones. Patients' stereoperception, color vision, and contrast sensitivity remained unaffected. In 96% of the patients' field of view, correct and exact answer was recorded (category 1). In 2% of the patients, small errors were measured in the visual field (category 2). In the remaining 2% of the patients' visual field, either large errors or no recognition were obtained (Figure 2).
Method. An IOL with the EDOF profile engraved on its surface was fabricated and tested on an optical bench based on the Liou-Brennan5 human eye model. We compared it with available diffractive-based IOLs. Resolution targets were set at 30 and 60 cm, 2.5 m, and infinity, and images were photographed and measured (Figure 3). White light illumination was used, and the pupil size was 3 mm.
Results. In general, focal depth extension of more than 2.50 D was demonstrated. At 30 cm, the performance of both IOLs was similar; however, the EDOF IOL produced less glare effect. The same was true at infinity. For distances of 60 cm and 2.5 m, the performance of the EDOF IOL was better, resolving smaller features and reducing chromatic aberrations. The EDOF IOL functioned well for decentration up to 0.5 mm and for tilting up to 10°.
The unique EDOF technology for ophthalmic applications, including spectacles, contact lenses, and IOLs, provides a potential solution for presbyopia that is better than existing options. In addition to the correction of presbyopia, the proposed technology also corrects astigmatism (regular and irregular), myopia, and hyperopia. The solution does not reduce the visual field nor generate loss in contrast sensitivity or resolution. With a high energetic input to the retina plane, this technology also reduces chromatic, glare, and halo aberration effects. The EDOF performance is present at various levels of illumination, for pupil sizes of 2 to 5 mm and with a reduced sensitivity to decentration for contact lenses and to decentration and tilting for IOLs.
Michael Belkin, MD, is a Professor of Ophthalmology, Incumbent of the Fox Chair of Ophthalmology, and Director of Ophthalmic Technologies Laboratory at the Goldschleger Eye Research Institute, Tel Aviv University, Sheba Medical Center, Tel Hashomer, Israel. Mr. Belkin states that he is a consultant to and owns shares of Xceed Imaging, Inc. He may be reached at tel: +972 3 530 2956; e-mail: firstname.lastname@example.org.
Karen Lahav-Yacouel, MA, is a part-time optometrist at Xceed Imaging Ltd., Petach Tikva, Israel. Ms. Lahav-Yacouel states that she is a salaried employee and owns shares of Xceed Imaging, Ltd. She may be reached at tel: +972 3 9271297; e-mail: email@example.com.
Ido Raveh, MSc, is a project manager at Xceed Imaging, Ltd., Petach Tikva, Israel. Mr. Raveh states that he is a salaried employee and owns shares of Xceed Imaging, Ltd. He may be reached at tel: +972 3 9271297; e-mail: firstname.lastname@example.org.
Shai Ben Yaish, BSc, is a project manager at Xceed Imaging, Ltd., Petach Tikva, Israel. Mr. Ben Yaish states that he is a salaried employee and owns shares of Xceed Imaging, Ltd. He may be reached at tel: +972 3 9271297; e-mail: email@example.com.
Oren Yehezkel, MSc, is a part-time optometrist at Xceed Imaging Ltd., Petach Tikva, Israel. Mr. Yehezkel states that he is a salaried employee and owns shares of Xceed Imaging, Ltd. He may be reached at tel: +972 3 9271297; e-mail: firstname.lastname@example.org.
Zeev Zalevsky, PhD, is Associate Professor of Engineering, at Bar-Ilan University, Israel. Professor Zalevsky states that he is a consultant to and owns shares in Xceed Imaging, Ltd. He may be reached at tel: +972 3 7384051; e-mail: email@example.com.
Alex Zlotnik, MSc, is a project manager at Xceed Imaging, Ltd., Petach Tikva, Israel. Mr. Zlotnik states that he is a salaried employee and owns shares of Xceed Imaging, Ltd. He may be reached at tel: +972 3 9271297; e-mail: firstname.lastname@example.org.
- Callina, T, Reynolds TP. Traditional methods for the treatment of presbyopia: spectacles, contact lenses, bifocal contact lenses. Ophthalmol Clin of North Am. 2006;19:25-33.
- Radu S. New soft toric contact lenses; silicone hydrogel lens for astigmatism. J Oftalmologia. 2006;50:59-62.
- Zalevsky Z, Shemer A, Zlotnik A, Ben Eliezer E, Marom E. All-optical axial super resolving imaging using a low-frequency binary-phase mask. Opt Express. 2006;14:2631-2643.
- Zalevsky Z, Ben Yaish S, Yehezkel O, Belkin M. Thin spectacles for myopia, presbyopia and astigmatism insensitive vision. Opt Express. 2007;15:10790-10803.
- Liou H, Brennan NA. Anatomically accurate, finite model eye for optical modeling. J Opt Soc Am. 1997;14(8):1684-1695.